Carbon fiber from oriented vinylidene halide polymers

ABSTRACT

1. A PROCESS FOR PREPARING A CARBONACEOUS FIBER FROM A VINYLIDENE CHLORIDE POLYMER FILAMENT COMPRISING THE SEQUENTIAL STEPS OF: (1) TREATING SAID VINYLIDENE CHLORIDE POLYMER FILAMENT WITH AN ORGANIC AMINE HAVING THE FORMULA R-NH2 WHEREIN R IS ALKYL CONTAINING FROM 1 TO 4 CARBON ATOMS AT A TEMPERATURE LESS THAN ABOUT 125*C. IN THE ESSENTIAL ABSENCE OF MOISTURE UNTIL SAID FILAMENT IS FROM ABOUT 25 TO 80 PERCENT DEHYDROHALOGENATED BYT WUTHO OUT SIGNIFICANT LOSS IN FILAMENT STRUCTURAL INTEGRITY, AND (2) CARBONIZING SAID FILAMENT BY SUBJECTING THE SAME TO A TEMPERATURE WHICH IS INCREASED FROM AN INITIAL VALUE OF AT LEAST ABOUT 90*C. TO A FINAL VALUE OF UP TO ABOUT 1500*C. OVER A PERIOD OF AT LEAST 5 MINUTES.

United States Patent 'Oflice 3,840,649 Patented Oct. 8, 1974 ABSTRACT OFTHE DISCLOSURE 7 Claims:

A process for preparing carbonaceous fibers useful as V reinforcementfor plastic or metal materials by (1) partially dehydrohalogenating avinylidene halide polymer filament by reaction with an organic nitrogenbase material without significant destruction of filament structuralintegrity, then (2) heating the partially dehydrohalogenated polymerfilament under specified carbonizing temperatures.

BACKGROUND OF THE INVENTION It is known that vinylidene chloridepolymers are capa ble of being carbonized. In this regard, US. Pat.3,516,- 791 discloses a method of carbonizing polyvinylidene chloride inpowder or film form wherein the polymer" is initially at least partiallydehydrohalogenated-by treatment with an alkali metal amide in liquidammonia. The materials produced are highly porous and adsorptive and arethus useful as molecular sieves. Such materials, however, are not usefulfor the type of reinforcement of plastic or metal materials where carbonfibers are employed.

It is also known to prepare carbon fibers by controlled thermaldecomposition of fibers prepared from copolymers of vinylidene chlorideand vinyl chloride, e.g., as set forth in the article entitledPreparation and Structure of Saran-Carbon Fibers, by E. A. Boucher, R.N. Cooper and D. H. Everett, published in Carbon, 1970, vol. 8, pp.597-605.

Utilization of thermal dehydrohalogenation techniques are generallyundesirable due to a difiicultly controlled initiation of thedehydrohalogenation reaction with accompanying lack of reproducibilityin results and subsequent melting and burning of the fiber.

It is also known that vinylidene chloride polymer, in film form, may bediscolored by reaction with amines, e.g., as set forth in Kogyo KagakuZasshi, 71 (8), 1272- 1276 (1968).

Heretofore, however, a practical method of preparing carbonaceous fibersfrom'vinylidene halide polymer filaments, which fibers are useful asreinforcement for plastic or metal materials, has not been known.

SUMMARY carbonaceous fibers which are particularly useful as polymer ofpure vinylidene chloride or copolymers of vinylidene chloride andvinylidene bromide or copolymers thereof with other polymerizablematerials wherein the portion of vinylidene halide is at least aboveabout 60 percent and preferably above about 80 percent by weight. Thesepolymers are crystalline and show the characteristic X-ray diffractionpatterns known as fiber patterns. These fiber patterns occur when apolycrystalline body is made up of a collection of single crystals allhaving one crystal axis essentially parallel to one direction called thefiber axis but with the other two axis oriented at random from onecrystal to the next. Although the complete structure of polyvinylidenechloride has not been precisely determined, all researchers agree thatthe polymer chain lies along one axis (usually called the monoclinicb-axis) parallel to the fiber direction. Articles so characterized havea higher tensile strength in the fiber direction than unoriented bodies.

Most of the materials copolymerizable with vinylidene halides do not inthemselves exhibit characteristic X-ray patterns and many of thecopolymers of the vinylidene halides containing large proportions ofthese materials are similarly incapable of being drawn into strong,pliable articles. There is, then, an upper limit of the amount ofmaterial copolymerized with the vinylidene halides for the purposes ofthe present invention. In the case of most copolymers of such vinylidenehalides, there should be no greater than about 40, and usually less than15 to 20 percent 'of the other polymerizable component. Thecopolymerizable materials include vinyl chloride, vinyl acetate,styrene, ethyl acrylate, acrylonitrile, methyl acrylate, methylmethacrylate, and many other copolymerizable compounds.

In the process of the present invention the vinylidene halide polymerfilament is initially treated at a temperature of less than 125 C. withan organic nitrogen base to induce dehydrohalogenation with resultantcreation of carbon to carbon double bonds along each polymer chain. Thistreatment permits dehydrohalogenation of the vinylidene halide polymerfilament to be rapidly completed (by heating) without loss of thestructural integrity of the filament.

reinforcement for plastic materials are prepared by a process comprisingthe sequential steps of:

(l) Treating an oriented vinylidene'halide polymer filament with anorganic nitrogen base material at a temperature less than about 125 C.innthe. essential ab.

sence of moisture until the filament is from about 25 to percentdehydrohalogenated but without significant loss in filament structuralintegrity, and

(2) Subjecting the filament to a temperature which is increased from aninitial value of at least about C. to a final value of up to about 1500C. over a period of at least 5 minutes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this regard, it has beenfound that any organic nitrogen base which blackens an orientedvinylidene halide polymer filament or film which is immersed in it at atemperature of about 50 C.,in about 60 minutes or less may be used.Exemplary of the preferred bases are the organic nitrogen bases such asamines having the formula RNH wherein R is alkyl or alkenyl containingfrom 1 to 4 carbon atoms, such as methyl amine, ethyl amine, propyl,allyl and butyl amines. Also preferred is the cyclic imine, pyrrolidine.Other materials which may be used include the guanidines such asguanidine, l-amino guanidine, tetramethyl guanidine and diethylguanidines; aziridines; aromatic and nonaromatic N-heterocycles; methylhydrazines; and the alkanol amines such as 3-amino-lpropanol,l-amino-Z-propanol, 2-arnino ethanol and pyrrole.

' The nitrogen base treatment may be accomplished by immersing thefilament in a liquid base material as such, or in'admixture with aninert diluent, or by exposing the filament to a gaseous base material.When using liquid nitrogen base materials, such materials are generallymaintained at a temperature of from about 20 C.

to 50 C. with a residence time of the filament in the base materialgenerally ranging from about 0.1 to 30 minutes, depending ontemperature, filament diameter and the base used. It is also preferableto conduct the dehydrohalogenation reaction in the essential absence of'contactbetween the nitrogen base material and moisture for optimumefliciency. It is also preferable that the fiber is rinsed with asolvent, such as isopropyl alcohol, upon removal from the nitrogen basebath.

The partially dehydrohalogenated filament is then heated, under atemperature which is increased from an initial value of at least about90 C. over a period of 4 Each of the polymer filaments designated asSample Nos. 1 through 10 (with the exception of Sample No. 9) on Table Isupra, were subsequently heated in the presence of nitrogen from atemperature of from 90 C. to 1000 C. over a period of about 70 minutes.The filament desigat least 5 minutes to a final value of up to 1500 C. 5nated as Sample No. l (non-dehydrohalogenated) melted The carbon fibersoptionally can then be graphitized before carbonizing. By way ofcomparison, each of the to any desired extent by heating the carbonfiber to a filaments designated as Sample Nos. 2 through 8 andtemperature between about 1500" C. and 3000 C. Gen- Sample N0. 10 formedstrong, flexible carbon fibers. erally, the carbon fiber requiresexposure to such tem- 10 Series H perature for a period of at leastabout 10 seconds. In the use of electrical self-heating of a carbonfiber tow, Batch dehydrochlorination reactions on separate 0.0015 careshould be taken to have a sufficient number of fibers inch diameter 30filament tow samples of same copolypresent in order to generate theneeded graphitization mer as Series I, wherein each sample wasdehydrochloritemperatures. For example, a single 0.010 inch diameternated as set forth on the following Table II.

TABLE II Batch dehydrochlorination reactions on a thirty filament tow oforiented vinylidene chloride polymer (0.0015 inch diameter) Series IIProperties of dehydrochlorinated filament Chemical treatment TensilePercent Temp. Time strength Elongation Modulus Sample numberDehydrochlorinationagent 0.) (min.) (p.s.i. 10 (percent) (p.s.i. l0) 001 N 11 N 41 61 0. 13 12- 10% 0311mm in DMSO'..- 23 90 N.D. N.D. N.D.N.D. N.D. N.D 13- 10% CaH NH in DMS0 23 150 N.D. N.D. N.D. N.D. N.D.N.D. 14 0 11mm 23 11 N.D. N.D. N.D. N.D. N.D. N.D. 15- 0=H1NH, 2a 10 220. 39 39.2 56.2 1.6

l DMSO=DimethylsnlIoxide. 2 N.D.=Not Determined.

fiber is enough at volts, applied potential, but about 10 or 15 fibersare needed, even at 140 volts applied potential, if the diameter is0.0015 inch.

It is often desirable to maintain the filament under shrink resistingtension, particularly when such filament is heated to temperatures aboveabout 100 C. Further, it may be desirable to apply tension sufiicient toelongate the filament somewhat during the carbonization thereof.

It is to be understood that the process of this invention may beconducted batchwise or in a continuous manner utilizing conventionallyemployed equipment.

The following nonlimiting examples will further serve to illustrate theinvention.

EXAMPLE I The following individual experiments were conducted asfollows:

Series I Batch dehydrochlorination reactions on 0.010 inch diametermonofilament of a copolymer of about 85 weight percent vinylidenechloride and about 15 weight percent vinyl chloride.

Each sample was individually wound onto a glass frame and immersed inone of several chemical treatment compounds for specified times atspecified temperatures.

The following Table I sets forth the chemical treating compounds used,the dehydrochlorination reaction conditions used and the extent ofreaction.

Series III Continuous dehydrochlorination reactions on separate 0.0015inch diameter 30 filament tow samples of the same copolymer as Series Iand II wherein each sample was dehydrochlorinated by being continuouslydrawn at constant length through a bath of the specified chemicaltreating compound.

Series III A Continuous dehydrochlorination as above but fibers allowedto shrink during amine treatment to 52% of initial length.

TABLE I Batch dehydrochlorination reactions on oriented vinylidenechloride polymer filament (0.010 inch diameter) Series I Properties 01.dehydrochlorinated filament Chemical treatment Percent Dehydroensilechlorination Temp. Time s rength Elonga- Sample number agent 0.) (minp.s tion 0 Cl N 1 None 23 70.6 CsH'INHI 23 10 l N.D. N.D. N.D. 63. 2N.D. CaH1NH1 23 20 24 16 N.D. 69. 5 N.D. CsH7NH 23 30 20 25 N.D. N.D.N.D. C H NH, 47 0. N.D. N .D. N.D. N .D. N.D. C3H7NH2 47 1 N.D. N .D.N.D. 59 N.D. CsH NH2 47 1.5 N.D. N.D.- N.D. N.D. N.D. C,H1NH; 47 2 N.D.N.D.- 33. 4 68. 4 1. 0 CaH1NH 47 3 N.D. N.D.- 42. 8 50. 1 2. 9 C4HQNH123 15 N.D. N.D. N.D. .D. N.D.

l N .D.=Not Determined.

The following Table III identifies the fiber samples used and. thetechniques and conditions employed:

eating a fiber of previously unknown composition and structure.

TABLE III Continuous dehydroehlorination reactions on a thirty filamenttow vinylidene chloride polymer (0.0015 inch diameter) Series IIIChemical Treatment Properties of dehydrochlorinated filamente TensileElon a- Tensile I P Dehydrochlorina- Temp. Time strength ti%n modulusement Sample number tlon agent C.) (min.) (p.s.i. 10 (percent) (p.s.i.10 Cl N 16 CaH1NH2 23 12 26 25 0.42 35.6 60.2 i 1.0 23 1o N.D. N.D. N.D.34. 2 62. 2 0. s

23 r 9 37 19 0. 42 34. 4 e2. 4 0. e

23 8. 5 N.D. N.D. N.D. 32. 7 63. 2 6.1

Series III-A Csfl- NHr 23 14. 3 N.D N.D. N.D. a7. 9 56.8 1.7

crH NH 23 20. s 14 42 0. 24 55. 1 35. 2 4. 7

C3H7NH1 23 25. 5 31 0. 59. 0 29. 8 6. 0

CzH NHg 23 51. 5 36 23 0. 60 60.7 27. 6 6. 2

1 N .D.=Not determined.

Each of the P y filaments designated as Sample The following Table Vsets forth the conditions used to Nos. 16 through 24 of Table III weresubsequently heated 25 graphitize th Samples f T bl IV, h i th b nin thePresence of nitrogen from a temperature of from ized fiber is passedthrough a graphitization furnace. 90 C. to 1000 C. over a period ofabout 70 minutes and all formed strong, flexible carbon fibers.

The following Table IV sets forth conditions used for ABLE Vcarobnization of samples representing the present inven- Gra hitlzationof ca bomzed Vin lid ne ehlorlde ol er fibers tlon as presented m TableH (Sample No. 15) and Table p r y e ym III (Samples 18 and 20), whereinthe partly dehydro- Sam le deslgnatiou chlorinated samples were heatedunder tension at specified 32 33 v 34 (sam le (sam is (sampletemperatures and tlme. Table TV A is for a slmllar $601188 35 25 g 26 m27 from but with a maximum carbomzatlon temperature of 900 C. Table IV)Table IV Table IV) TABLE IV Tension Carbonization of partlydehydrochloriuated vlnylidene chloride polymer gfif gg gg fiif 'zbj'fgk'f i: 8g 3g fibers gilber nllodulus (p.s.i. (l0) g i er 0 on ationercel'lt Sample deslgnetwn 40 Percent oa ibonui f 99.5 100 98.9

26 27 (Sample (Sample (S mp1 6 1 Tension is 10 grams per 30 filamenttow. 15 from 18 from 20 from Table Table Table 11) III) III) Tension 1 r(2) What is claimed is:

ribii 8 a vinylidene chloride polymer filament comprlslng the 1lzereentcfibqn 3 N.g. N.B. ti l Steps of;

Yamagata; fig fig 038 1 treating said vinylidene chloride polymer filamn Tensionis 10 grams per 30 filament tow with an organic amine havingthe formula RNH Fibers held at constant length by winding around agraphite block wherein R 15 alkyl Contammg from 1 to 4 carbqn iffs i faatoms at a temperature less than about 125 C. 1n

the essential absence of moisture until said filament TABLE IV-A is fromabout 25 to 80 percent dehydrohalogenated Carbonization of partlydehydroehlorinatedvinylidenechloride polymer P Without Slgmficant 1055 mfilament Structural fibers integrity, and

Sample Designation (2) carbonizing said filament by sub ecting thesame28 29 30 31 to a temperature which is increased from an lnltlal (sample(sample (sample (sample value of at least about 90 C. to a final valueof 21 from 22 from 23 from 24 from e Table Table Table Table up to about1500 C. over a period of at least 5 III-A) III-A) III-A) III-A) minutes.h d I d 2. The process of Claim 1 w erein sai vlnyl ene l l l 1 gg fis-aO O O O chloride polymer is a copolymer of vmylldene chloride (m nut 2020 20 20 and vinyl chloride s'l h ai s b2 135???" 33 37 44 70 3. Theprocess of Claim 2 whereln sald vlnylldene chloride polymer is acopolymer of about 85 weight percent 10') 1. 68 1. 92 2. 04 2. 51

Fiber elongation vlnylldene chlorlde and about 15 welght percent ofvlnyl g i) g-g g chloride.

6 11 car OH.-. Pei nt cl 1lorlne 12.9 N.D. 10 N.D. 4. The process ofClaim 1 whereln sald organlc amlne Percent mtmgen 70 is selected fromthe group consisting of propylamlne and l Tension is 10 grams per 30filament tow. bu'tyl amine. i

Detenmned- 5. The process of Claim 1 wherein said filament 1s It will benoted from Table IV A that the carbonized carbonized by subjecting thesame to a temperature of fibers contain significant amounts of nitrogenand chlofrom about 900 C. to 1000 C. for a period of from rine, i.e.,even after being heated to 900 C., thus indiabout 10 to 20 minutes.

7 8 6. The process of Claim 5 wherein said filament is OTHER REFERENCEScarbonized while in a substantially nonoxidizing environ- Boucher,chemical Abstracts, VOL 7 4, June 28, 1971, ment. 14314911.

7. The process of Claim 1 containing in addition thereto KirkDthmetEncyclopedia of Chemical Technology, and in combination therewith thestep of graphitizing the 5 2nd VOL 21 1970 carbonized filament byheating said filament to a ternwolkober ahemialAbstracts 62 1965 690eperature between about 1500" C. and 3000 C. for a Boucher al' (In,Carbon, 1 8 5, November period of at least about 10 seconds. 1970, pp.597-605.

References Cited 10 EDWARD J. MEROS, Primary Examiner UNITED STATESPATENTS 3,516,791 6/1970 Evans et al. 423 449 FOREIGN PATENTS 26429;423-448, 449

2,038,915 2/1971 Germany' 423-447 15

1. A PROCESS FOR PREPARING A CARBONACEOUS FIBER FROM A VINYLIDENECHLORIDE POLYMER FILAMENT COMPRISING THE SEQUENTIAL STEPS OF: (1)TREATING SAID VINYLIDENE CHLORIDE POLYMER FILAMENT WITH AN ORGANIC AMINEHAVING THE FORMULA R-NH2 WHEREIN R IS ALKYL CONTAINING FROM 1 TO 4CARBON ATOMS AT A TEMPERATURE LESS THAN ABOUT 125*C. IN THE ESSENTIALABSENCE OF MOISTURE UNTIL SAID FILAMENT IS FROM ABOUT 25 TO 80 PERCENTDEHYDROHALOGENATED BYT WUTHO OUT SIGNIFICANT LOSS IN FILAMENT STRUCTURALINTEGRITY, AND (2) CARBONIZING SAID FILAMENT BY SUBJECTING THE SAME TO ATEMPERATURE WHICH IS INCREASED FROM AN INITIAL VALUE OF AT LEAST ABOUT90*C. TO A FINAL VALUE OF UP TO ABOUT 1500*C. OVER A PERIOD OF AT LEAST5 MINUTES.